This invention relates to the signal transmission technique. Particularly, this invention relates to the method for demodulating the signal of multiple frequency manipulation with equidistant frequency spreading, respective demodulator, and computer-readable medium with the program for implementing this method.
At present, various devices for demodulating the signal of multiple frequency manipulation with equidistant frequency spreading used in the transmission technique are well known.
Thus, the U.S. Pat. No. 6,671,333 (published Dec. 30, 2003) discloses, particularly, the demodulator for such a signal, being, in fact, a usual frequency detector (demodulator) that has a very significant demodulation threshold.
From the RU Patent No. 2232479 (published Jul. 10, 2004) the Method and system for transmitting and receiving the signals of multiple frequency manipulation with equidistant frequency spreading are known. However, these method and system are characterized by an increased complexity because, while receiving, they require an additional step of forming the signal peaks indicating the borders of every symbol.
The U.S. Pat. No. 6,697,440 (published Feb. 24, 2004) also discloses the demodulator of the signal of interest.
The most often used at present is the quasi-optimal demodulator. For example, the U.S. Pat. No. 4,518,922 (published May 21, 1985) discloses the demodulator for the signal of multiple frequency manipulation with equidistant frequency spreading, which demodulator comprising m quadrature channels, where m is the maximum number of quadrature frequencies in the signal of multiple frequency manipulation with the equidistant frequency spreading, every quadrature channel comprising the first and second multipliers, which outputs being connected with the inputs of the first and second low-pass filters, respectively, the first inputs of all multipliers of all quadrature channels being the united input of the demodulator, in every quadrature channel the second input of the first multiplier is connected with the output of the phase shifter by 90°, which input is united with the second input of the second multiplier and is the reference input of this quadrature channel; the frequency former, which each of m outputs is connected to the reference input of the respective quadrature channel; the decision unit which outputs are the demodulator outputs.
The same U.S. Pat. No. 4,518,922 disclose also the method for demodulating the signal of multiple frequency manipulation with equidistant frequency spreading, which method comprises the steps of: forming the array of adjustable frequencies from f1 to fm, where m is the maximum number of the frequencies in the signal of multiple frequency manipulation with equidistant frequency spreading fp=kft, where ft is the clock frequency, k=1, 2, . . . , the initial frequency values in said array being allocated approximately in those regions, where the exact values of the frequency of the received signal could be situated; demodulating the received signal using said formed frequency array.
However, the known quasi-optimal demodulator still has the demodulation threshold that is 3 dB higher than the optimal one.